Lifeblood of the Forest restores him to full Health. High Status Resist while casting, so Knockback is a better bet. Appears to only cast it once per encounter, so most you have to do is kill him twice to get him to stay dead.

I just kept hitting him. He never tried to heal. I used cleansing pot right before he did his 4th stack of petrify, stunned him whenever, but saved my smoke bomb in case he tried to heal. If he used his armor booster, I used a purge rune. Wasnt too hard.